1. Field of the Invention
This invention relates to a blackbody furnace with a favorable temperature distribution which is utilized for calibration and the like for radiation thermometers.
2. Description of the Prior Art
Heretofore, conventional blackbody furnaces having a large aperture diameter could not be a perfect blackbody having an effective cavity emissivity of unity due to the influences of the apertures, even if the inner wall of the cavity of such blackbody furnaces has a uniform temperature. For this reason, in such conventional blackbody furnaces, three-zone control means having a main heater is disposed on the targets of a cylindrical blackbody furnace as well as two auxiliary heaters which are disposed in the vicinity of opposite apertures thereof, respectively, and the temperatures of the respective auxiliary heaters are raised to correct energy emitted from the apertures. However, such amount of energy to be compensated varies dependent upon measurement temperatures or measurement wavelengths, and therefore it is difficult to always utilize such conventional cylindrical blackbody furnaces as the optimum blackbody furnaces.
Furthermore blackbody furnaces are indispensable instruments for calibrating radiation thermometers and the like, so that a blackbody furnace having a favorable temperature distribution has heretofore been required in this respect.
On one hand, a temperature generator suitable for application to spherical blackbody furnaces is proposed in Japanese Patent Application No. 62973/80. In this case, a heating member is divided into the upper, lower and side surfaces, and temperature control thereof is carried out in such conditions, but it became clear that compensation for temperature drop at the aperture surface side in such spherical blackbody furnaces was particularly difficult. In such case, even if the density of heat generation in the aperture surface side of the spherical blackbody furnaces is elevated, it is difficult to effect a well-balanced temperature control extending over the whole region of measured temperatures.